A Bugzilla Security Advisory reports:

Cross-Site Request Forgery

When a user submits changes to a bug right after another
user did, a midair collision page is displayed to inform
the user about changes recently made. This page contains
a token which can be used to validate the changes if the
user decides to submit his changes anyway. A regression
in Bugzilla 4.4 caused this token to be recreated if a
crafted URL was given, even when no midair collision page
was going to be displayed, allowing an attacker to bypass
the token check and abuse a user to commit changes on his
behalf.

Cross-Site Request Forgery

When an attachment is edited, a token is generated to
validate changes made by the user. Using a crafted URL,
an attacker could force the token to be recreated,
allowing him to bypass the token check and abuse a user
to commit changes on his behalf.

Cross-Site Scripting

Some parameters passed to editflagtypes.cgi were not
correctly filtered in the HTML page, which could lead
to XSS.

Cross-Site Scripting

Due to an incomplete fix for CVE-2012-4189, some
incorrectly filtered field values in tabular reports
could lead to XSS.

A Bugzilla Security Advisory reports:

Dangerous control characters can be inserted into
Bugzilla, notably into bug comments. If the text, which
may look safe, is copied into a terminal such as xterm or
gnome-terminal, then unexpected commands could be executed
on the local machine.

A Bugzilla Security Advisory reports:

The login form had no CSRF protection, meaning that
an attacker could force the victim to log in using the
attacker's credentials. If the victim then reports a new
security sensitive bug, the attacker would get immediate
access to this bug.

Due to changes involved in the Bugzilla API, this fix is
not backported to the 4.0 and 4.2 branches, meaning that
Bugzilla 4.0.12 and older, and 4.2.8 and older, will
remain vulnerable to this issue.